with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a multi-peak
structure with a duration of about 80 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~20 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+47.2
minutes. There will be no XRT or UVOT data until this time.
Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

GCN Circular #16143
L. Elenin (KIAM), A. Volnova (IKI), I. Molotov (KIAM), A. Pozanenko (IKI)
report on behalf of larger GRB follow-up collaboration:
We observed of the field of the Swift GRB 140423 (Sonbas et al., GCN
16142) with 0.4-m telescope of ISON-NM observatory starting
on Mar., 20 (UT) 09:01:03. The start of observation was delayed due to bad
weather. We took unfiltered images of 30 s exposures. We detect a fading
optical source in coordinates
(J2000) 13 09 08.50 +49 50 29.4
(with initial accuracy of about 1 arcsec). Preliminary photometry of the
source in the first images is ~ 17.2m. the photometry is based on nearby
USNO-B1.0 stars (R2 mag). Since the source is absent in USNO-B1.0 catalog
and clearly fading we suggest it as GRB 140423 afterglow candidate.

This source is not visible in DSS (second epoch), 2MASS or the MPChecker database.
The object decayed from ~14.2 magnitude to ~15.0 magnitude in ~100 seconds.
A jpeg image is available at http://www.rotse.net/images/gsq596901_3b01_img.jpg
Continuing observations are in progress.

with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 98 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.09 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.4
(+2.57/-1.42) x 10^21 cm^-2 (90% confidence).

GCN Circular #16147
M. M. Chester (PSU), E. Sonbas (NASA/GSFC/Adiyaman Univ.), K. L. Page
(U Leicester), D. Malesani (DARK/NBI), and S. R. Oates (UCL-MSSL)
report on behalf of the Swift/UVOT team:
Swift/UVOT took a finding chart exposure of 150 seconds with the White filter
starting 2946 seconds after the BAT trigger. A faint source (19.6 +/- 0.4 mag)
is detected in the White filter which is consistent with the candidate reported
by Elenin et al. (GCN Circ. 16143) but not consistent with the Swift/XRT position
reported by D. N. Burrows et al. (GCN Circ. 16146). The separation from the XRT
position is 9.6 arcsec. The preliminary UVOT position is

RA (J2000) 197.28546 (13:09:08.51)
Dec (J2000) 49.84133 (+49:50:28.8)

with an estimated uncertainty of 1.1 arcsec (radius, 90% confidence,
statistical + systematic). No correction has been made for the
expected extinction corresponding to E(B-V) of 0.01.

The photometry is based on star SDSS J130858.37+494547.9 (assuming R =
15.418 +/- 0.018).
The finding chart of GRB 140423A afterglow can be found in
http://grb.rssi.ru/GRB140423A/GRB140423A_ISON-NM_fc.png
Also we report the corect time of observation of the first image in GCN
16143. It should be April, 23, (UT) 09:01:03.
We apologize for the misprint.

GCN Circular #16152
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:
"At 08:32:38.54 UT on 23 April 2014, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 140423A (trigger 419934761 / 140423356)
which was also detected by the Swift/BAT (Sonbas et al. 2014, GCN 16142)
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 44 degrees.
The GBM light curve shows a multiple-peak structure
with a duration (T90) of about 95 s (50-300 keV).
The time-averaged spectrum from T0-61.440 s to T0+32.768 s is
best fit by a Band function with Epeak = 125 +/- 9 keV,
alpha = -0.25 +/- 0.11, and beta = -1.97 +/- 0.06.
The event fluence (10-1000 keV) in this time interval is
(2.0 +/-0.1)E-05 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+5.44 s in the 10-1000 keV band
is 3.0 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

with an uncertainty of 1.4 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.

with an estimated uncertainty of 0.48 arc sec. (radius, 90% confidence).
This position is consistent with the enhanced XRT position reported by
Beardmore et al. (GCN Circ. 16155).
Preliminary detections and 3-sigma upper limits using the UVOT photometric
system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are:

with an uncertainty of 1.0 arcmin, (radius, sys+stat,
90% containment). The partial coding was 39%.
The mask-weighted light curve shows a multi-peak episode
starting ~T-50 sec, highest peak at ~T+45 sec, and the episode
ends around ~T+140 sec. T90 (15-350 keV) is 134 +- 23 sec
(estimated error including systematics).
The time-averaged spectrum from T-130.13 to T+108.91 sec
is best fit by a simple power-law model. The power law index
of the time-averaged spectrum is 1.33 +- 0.06. The fluence
in the 15-150 keV band is 9.4 +- 0.3 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+44.19 sec in
the 15-150 keV band is 2.1 +- 0.2 ph/cm2/sec. All the quoted
errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/596901/BA/

GCN Circular #16162
A. Amaral-Rogers (U. Leicester), K.L. Page (U. Leicester) and E. Sonbas
(NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift-XRT team:
We have analysed 11 ks of XRT data for GRB 140423A (Sonbas et al. GCN
Circ. 16142), from 3.0 ks to 40.0 ks after the BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Beardmore et al. (GCN Circ. 16155).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.00 (+/-0.05).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.08 (+/-0.09). The
best-fitting absorption column is 5.0 (+2.0, -1.8) x 10^20 cm^-2, in
excess of the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.1 x 10^-11 (3.6 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:

If the light curve continues to decay with a power-law decay index of
1.00, the count rate at T+24 hours will be 0.027 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.5 x
10^-13 (9.8 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00596901.
This circular is an official product of the Swift-XRT team.

The photometric error is dominated by calibration and is 0.07 mag (in r')
rms for a secondary reference star ensemble (but not accounting for color
terms or galactic foreground extinction).
The photometric calibration is based on
(i) cross-correlating with the sdss dr9 star catalog in the r' band over
the entire field of view (24' X 24')
(ii) consistency check on exemplary star SDSS J130915.57+494948.5 at sdss
r' = 19.98. The photometric error based on this reference star is < 0.02
mag rms.

GCN Circular #16166
P. D'Avanzo, S. Covino, D. Malesani, A. Rossi, G. Tagliaferri on behalf of the CIBO report:
We observed the field of GRB 140423A (Sonbas et al., GCN 16142) using the NICS
near-Infrared camera on the 3.6m TNG Telescope (La Palma, Canary Islands).
We obtained a series of imaging observations in the J, H and K' bands(16 minutes per filter)
at a mean epoch of 14.8 hours from the burst. The GRB afterglow is clearly detected in all bands.
The observed J-band magnitude is 19.7 +- 0.1 (calibrated against the 2MASS catalogue).

GCN Circular #16167
J. Takahashi and A. Arai (Univ. of Hyogo)
report on behalf of the Nayuta team and the OISTER collaboration:
We observed the field of GRB 140423A (Sonbas et al., GCN 16142)
with Nishiharima Infrared Camera (NIC) attached to the Nayuta 2-m
telescope at the Nishi-Harima Astronomical Observatory.
The observations were conducted on 2014-04-23 at 10:05-10:29 UT and
13:03-13:53 UT.
We detected the near-infrared afterglow in H and Ks bands.
Photometric results of our observations are listed below.
We used 2MASS 13085994+4951082 as a reference star for photometry.

Our photometry has been calibrated using an SDSS star in the FOV
(13:09:09.56 +49:52:13.38, r=3D19.76 +- 0.02, i=3D19.23 +- 0.02, z=3D18.9=
2 +-
0.04), it has not been corrected for foreground extinction, and the error=
s
include the uncertanity in the SDSS calibration star.
Comparing our observations with those in the GCNs, we derive a decay
constant of alpha~-1.0 relative to the photometry published by Cenko &
Perley (GCN 16153;
=E2=80=8Bfrom =E2=80=8B
+1.4 hr to +15 hr), and alpha~-1.2 relative to the z-band photometry
published by Maehara et al. (GCN 16151;
=E2=80=8Bfrom =E2=80=8B
+2hr to +15.8 hr) and the R-band photometry published by Pandey et al. (GCN
16164;
=E2=80=8Bfrom =E2=80=8B
+6 hr to +15 hr), where a colour term of r-Rc~0.19 has been assumed in the
latter. These decay rates are slower than those derived from the early
KAIT observations (Zheng et al., GCN 16156), who find alpha~-1.7 up to
about 6000 s.

These magnitudes are in the AB system and are not corrected for
Galactic extinction in the direction of the GRB.
We thank the staff of the Observatorio Astron=C3=B3mico Nacional in San
Pedro M=C3=A1rtir.

GCN Circular #16171
K. Gazeas & K. Sapountzis (National University of Athens) report:
We performed photometric observations on GRB140423A (trigger 596958)
in R band (optical), using the University of Athens Observatory (0.4 m
f/8 Cassegrain Reflector, equipped with a ST10XME CCD camera).

We also conclude that the trigger is consistent with the flare star DG
CVn , although we cannot exclude the possibility of being a field GRB.
Nevertheless, photometry of DG CVn reveals significant enhancing at
the OT and subsequent fading of the flare indicating an interesting
stellar activity. The photometric variability of the DG CVn with
respect to the field standard star GSC 2003:0711, shows a gradual
decay with a rate of 0.92 mag/hour for the first hour of observation
after the peak (23:30-00:30 UT), followed by a decay rate of 0.34
mag/hour for the rest 2.5 hours of observation (00:30-03:00).
[GCN OPS NOTE(25apr14): This circular was delayed ~5 hours until
and entry in the vetted list was created.]

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. Compared to our observations last
night (Littlejohns et al., GCN 16170), the source has faded approximately
as t^(-1.3).
We thank the staff of the Observatorio Astron=C3=B3mico Nacional in San Pedro
M=C3=A1rtir.